The function of a voltage regulator is to provide a predetermined and substantially constant output voltage in response to an unregulated input voltage. Two types of voltage regulators are commonly used including linear regulators and switching regulators.
A linear regulator typically controls the output voltage by controlling a voltage drop across a power transistor, which is connected in series with a load. The power transistor is generally operated in its linear region and conducts current continuously.
A switching regulator typically controls the output voltage by using a power transistor as a switch to provide a pulsed flow of current to a network of inductive and capacitive energy storage elements, which smooth the switched current pulses into a continuous and regulated output voltage. The power transistor may be operated either in a cutoff or saturated state at a duty cycle as needed by the voltage differential between the input and output voltages. Varying the duty cycle or frequency varies the regulated output voltage of the switching regulator.
Generally, a duty cycle of a switching regulator may be controlled by monitoring the output voltage or current through a switch. The latter type of switching regulator is known as a current-mode switching regulator, and is easier to frequency stabilize and has better response to transients than does a switching regulator in which the duty cycle is controlled directly by the output voltage.
Switching regulators have at least two advantages over linear regulators. First, switching regulators typically operate with greater efficiency than linear regulators, a particularly important factor in high current regulators. Second, switching regulators are more versatile than linear regulators. Switching regulators can provide output voltages which are less than, greater than, or of opposite polarity to the input voltage, depending on the mode of operation of the switching regulator, whereas linear regulators can only provide output voltages which are less than the input voltage.
Switching regulators, although more flexible than linear regulators in circuit applications, are typically more complex than linear regulators. Frequency control and regulation in voltage control systems for sensitive applications may have less than desirable accuracy and reliability. Especially, regulation during initial power up has proven to be difficult to control, when power supply voltages have not yet stabilized under a sudden load.
Thus, it is with respect to these considerations and others that the present invention has been made.